1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to securing mechanisms for electrical switching apparatus, such as draw-out circuit breakers.
2. Background Information
Electrical switching apparatus used in power distribution systems are often mounted within a switchgear enclosure either individually or in combination with other switchgear (e.g., without limitation, circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters, motor controllers and other load controllers).
Some electrical switching apparatus such as, for example, some medium-voltage and low-voltage circuit breakers, can be relatively large. In order to facilitate movement (e.g., installation; removal; maintenance), some circuit breakers are commonly coupled to draw-out mechanisms which permit such circuit breakers to be drawn out of the switchgear enclosure. Accordingly, such circuit breakers are commonly known in the art as “draw-out” circuit breakers. The circuit breaker may be further supported within a draw-out frame, commonly known in the art as a cassette or chassis. The switchgear enclosure generally includes a number of cells, with each cell being structured to receive a corresponding circuit breaker. The draw-out mechanism includes, for example, a combination of rails and rollers coupled to one or the other, or both, of the sidewalls of the cell and the sides of the corresponding circuit breaker, which is to be drawn into and out of the cell. Draw-out circuit breakers are described in further detail, for example, in commonly assigned U.S. Pat. No. 7,019,229, which is hereby incorporated herein by reference.
Under certain circumstances such as, for example, when the circuit breaker trips in response to an electrical fault condition (e.g., without limitation, a current overload; a short circuit; an abnormal voltage or some other fault condition), the circuit breaker may be subjected to relatively large magnetic repulsion forces. Such forces have a tendency to force the circuit breaker out of the cell of the switchgear enclosure. More specifically, the bottom of the circuit breaker is typically relatively secure, for example, by way of its connection to the draw-out mechanism. Accordingly, the magnetic repulsion forces, which are applied to the circuit breaker at some location above the relatively secure bottom, have a tendency to undesirably rotate the circuit breaker within the cell. To resist such rotation, it is desirable that the circuit breaker fits securely within the cell, with as little excess space between the circuit breaker and the cell, as possible.
The dimensions of switchgear enclosure cells can vary, making it necessary to measure the cell and then adjust the draw-out mechanism and/or the circuit breaker accordingly, in order to ensure that the circuit breaker is secure. One way this is known to be accomplished is by employing a plurality of bolts that must be adjusted (e.g., tightened; loosened) until they are brought into contact with a corresponding feature (e.g., without limitation, a bracket; a shelf; a ledge; a protrusion) of the switchgear enclosure in an attempt to resist the undesired movement (e.g., rotation) of the circuit breaker with respect to the cell. Among other disadvantages, measuring the cell and making the necessary adjustments to the circuit breaker and/or the draw-out mechanism is a time-consuming process. It also requires separate tools. This procedure can also be dangerous, for example, if the switchgear is energized at the time the measurements and/or adjustments are made.
There is, therefore, room for improvement in electrical switching apparatus, such as circuit breakers, and in securing mechanisms therefor.